Not everyone can offer constructive feedback, but most people can have the problems brought to their attention and understand them. Even if you had constructive criticism, how exactly would you go about alerting a developer at Apple?
Are these possibly from an earlier beta ?
If you run your phone with the display off, say from 21% battery down to 11%, then it will cross the 20% reporting threshold. The next time that you unlock the phone and activate the display, you will get the notification.
It's not inconsistent; nor is it just being "optimistic" -- it may be poorly worded, but it consistently displays that same message every time you unlock the phone after the battery drains to 20%.
If the person who took that screenshot had waited another ten minutes, then the battery would probably have reached 10%, and the 10% notification would have been shown instead.